When you're changing the "start at" number in the chapter numbering dialog, then the number won't be updated in the document until you click on "Format > Clear Direct Formatting" (Control + M) or you assign the same paragraph style to the text again.
In previous versions of LibreOffice, the number was updated automatically after closing the chapter numbering dialog with OK without any further user action.
Steps to reproduce:
1. Open a new Writer document.
2. Insert a short dummy text.
3. Change formatting of this text to paragraph style "Heading 1".
4. Set the cursor into this text.
5. Open Tools > Chapter Numbering...
6. Change "Number" field to what you want, "1, 2, 3, ..." for example.
7. Click OK to close the dialog. The text now has a number in front of it.
8. Open Tools > Chapter Numbering... again.
9. Change the "Start at" field to any other number, "5" for example.
10. Click OK to close the dialog.
The chapter numbering in the document should have changed to "5" as choosen by the user in the dialog.
Nothing. The chapter numbering didn't change and "1" is still visible.
Version: 188.8.131.52 (X86_64) / LibreOffice Community
Build ID: e8bf3b441b8370f8440b0339fd9490765a8d57ca
CPU threads: 12; OS: Windows 10.0 Build 19045; UI render: Skia/Vulkan; VCL: win
Version: 184.108.40.206.alpha0+ (X86_64) / LibreOffice Community
Build ID: 7a7eb4aa21ca0c83db825fe8d5a5278611b391d8
CPU threads: 4; OS: Linux 5.15; UI render: default; VCL: gtk3
Locale: cs-CZ (cs_CZ.UTF-8); UI: en-US
This seems to have begun at the below commit in bibisect repository/OS linux-64-7.5.
Adding Cc: to Noel Grandin ; Could you possibly take a look at this one?
7d0730a30f43c4648de8ed59b1cbc196f1120970 is the first bad commit
Author: Jenkins Build User <firstname.lastname@example.org>
Date: Fri Oct 14 18:59:35 2022 +0200
141373: tdf#129101 CTRL+A & Cut very slow | https://gerrit.libreoffice.org/c/core/+/141373